This invention relates generally to a method for preparing organosilicon compounds that contain silicon-bonded acylamino-substituted hydrocarbon radicals. More specifically, the method involves the reaction of aminoalkylsilanes and siloxanes with acyl halides in nonaqueous media in the presence of an aqueous acid acceptor with an additive to facilitate the phase transfer of the acid acceptor into the nonaqueous phase.
Organosilicon compounds that contain silicon-bonded acylamino-substituted hydrocarbon radicals are well known and have been described in U.S. Pat. No. 4,608,270 which is herein incorporated by reference.
As mentioned in Varaprath U.S. Pat. No. 4,608,270 and as taught in U.S. Pat. No. 2,929,829 to Morehouse, Japan 51/108022 to Furuya et al., Japan 56/74113 to Takamizawa and West German DE No. 2365272 to Koetzsch et al., acylaminoorganopolysiloxanes can be synthesized by reacting aminosiloxanes with the corresponding acid chloride in the presence of a tertiary amine such as triethylamine. However, such a synthesis has several disadvantages. First, the removal of the voluminous precipitate of triethylamine hydrochloride by filtration is tedious. Second, a small amount of HCl is liberated even when an excess of amine is used. This HCl is detrimental to the stability of the polymer, especially when the acid chloride has other reactive vinyl functionality such as where the acid chloride is acryl chloride.
An alternative method for the preparation for the acylaminoorganopolysiloxanes involves the reaction of aminosiloxanes and silanes with an acid anhydride or ester at elevated temperature. This is taught in U.S. Pat. No. 4,507,455 to Tangney and Ziemelis, assigned to the assignee of the present invention. Unfortunately at the elevated temperatures of the reaction, arcylamide derivatives undergo Michael addition and amidation of the acrylic double bond resulting in unwanted byproducts and crosslinkage of the desired product which ultimately causes the polymer to gel.
Finally as taught in the above-mentioned U.S. Pat. No. 4,608,270 to Varaprath, these problems can be overcome by reacting the aminosilanes and siloxanes with acid chlorides in the presence of aqueous sodium hydroxide. The HCl that is produced on addition of acyl chloride is neutralized by hydroxide in the aqueous phase. However, a problem arises from the fact that this reaction is carried out in a two-phase system in which the aminosiloxane is dissolved in an organic solvent that is immiscible with water. Because the amide function is generally highly polar and hydrophilic, it shows a great tendency to absorb moisture. Incorporation of these units into the siloxane backbone increases water miscibility causing the polymers to emulsify easily thus making phase separation difficult. To some extent, this problem can be overcome by using chlorinated solvents such as methylene chloride or chloroform but, unfortunately, such solvents are toxic.
It is thought that these solvents are effective because they typically contain substantial amounts, such as greater than 0.05 weight percent at ambient conditions, of dissolved water which serves to assist in the phase transfer of chloride ion byproduct from the nonaqueous to the aqueous phase.
Attempts to use non-toxic solvents other than chlorinated solvents have lead to gellation, poor conversion to product or poor phase separation.
Accordingly, the need remains for an improved method for preparing acylaminoorganosilicon compounds that avoids the phase separation and solvent toxicity problems previously encountered while simultaneously providing transfer of acid acceptor and salt by-product across the interface of a two-phase system.